In various medical imaging procedures it is beneficial to provide both an x-ray image and a nuclear image of a region of interest. The x-ray image typically provides structural information indicative of the anatomy of the region of interest. The nuclear image, defined herein to mean an image indicative of radiotracer distribution in an object, is generated based on detected gamma quanta. The nuclear image may for example be a gamma scintigraphy or a SPECT image and typically provides functional, or physiological information relating to the region of interest. Together the two different image types can be used to improve the identification of an underlying pathology during a medical investigation.
Various medical procedures also benefit from a combination of x-ray and nuclear imaging. Selective internal radiation therapy, or SIRT, is one such medical procedure in which radiation is used to treat cancer. SIRT is often used for non-resectable cancers, i.e. cancers that cannot be treated surgically, and involves injecting microspheres of radioactive material into the arteries that supply the tumor. Liver tumours or metastases are often treated in this way. However, in delivering such therapy, a number of workflow steps are required in order to prevent potential side effects. These steps may include the closure of atypical lung and gastrointestinal shunts before injection of Yttrium-90-containing microspheres. This prevents radiation ulcers which might otherwise be triggered by extra-hepatic localization of administered micro-spheres. For this purpose, catheter-based vessel coiling is performed under x-ray guidance during a minimally-invasive procedure. Afterwards, the remaining shunt level towards lungs and gastrointestinal area may be controlled by injection of Technetium 99mTc albumin aggregated, i.e. Tc-labeled MAA, into both main liver arteries followed by planar gamma imaging. During this procedure the patient is typically repeatedly transported between a cath lab and SPECT imaging room.
A need therefore exists for imaging systems that are capable of providing both a nuclear image and an x-ray image.
Document US2013/237818A1 discloses a radiation detector having a first detector layer and a second detector layer. Detectors of the first layer include scintillators and light detectors. The detectors of the second detector layer include scintillators and optical detectors. The scintillators of the first layer have a smaller cross-section than the scintillators of the second layers. A group of the first layer scintillators overlay each second group scintillator. In a CT mode, detectors of the first layer detect transmission radiation to generate a CT image with a relatively high resolution and the detectors of the second layer detect PET or SPECT radiation to generate nuclear data for reconstruction into a lower resolution emission image.
Document U.S. Pat. No. 6,448,559 B1 discloses a detector assembly for multi-modality PET/SPEC/CT scanners. The detector assembly comprises a first layer for detecting low energy gamma radiation and x-rays and a second layer for detecting high energy gamma radiation. The first layer is generally transparent to high energy gamma radiation. The detector assembly includes a photodetector in the form of an avalanche photodiode to transform the light signals from the scintillators into electric signals. The detector assembly may be incorporated in a multi-modality PET/SPECT/CT scanner for simultaneous transmission and emission imaging with the same detection geometry. In one example configuration a collimator is positioned in front of the detector assembly to define preferential incidence directions for SPECT photons.
However, in the field of medical imaging, and in the field of medical procedures, there remains a need for improved imaging systems that are capable of providing both a nuclear image and an x-ray image.